Method for manufacturing a liquid crystal display

ABSTRACT

A method for manufacturing a liquid crystal display is provided. The method includes the steps of forming a gate electrode and a gate pad by sequentially depositing a first metal film and a second metal film on a substrate of a TFT area and a pad area, respectively, by a first photolithography process, forming an insulating film on the entire surface of the substrate on which the gate electrode and the gate pad are formed, forming a semiconductor film pattern on the insulating film of the TFT area using a second photolithography process, forming a source electrode and a drain electrode composed of a third metal film in the TFT area using a third photolithography process, forming a protection film pattern which exposes a portion of the drain electrode and a portion of the pad on the substrate on which the source electrode and the drain electrode are formed using a fourth photolithography process, and forming a pixel electrode connected to the drain electrode and the gate pad on the substrate on which the protection film pattern is formed using a fifth photolithography process. By using this method it is possible to reduce the number of photolithography steps required for manufacture and to prevent a battery effect and generation of a hillock in the resulting structure.

This application is a continuation application of “METHOD FORMANUFACTURING A LIQUID CRYSTAL DISPLAY,” by Jeung-gil LEE et al., Ser.No. 08/754,644, filed on Nov. 21, 1996 now U.S. Pat. No. 6,008,065, thecontents of which are herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method for manufacturing a liquidcrystal display. More particularly, present invention relates to animproved method for manufacturing a thin film transistor-liquid crystaldisplay which reduces the number of photolithography processes that mustbe performed.

A thin film transistor LCD (“TFT-LCD”), which uses the thin filmtransistor as the active device, has various advantages over other LCDs.These advantages include low power consumption, low drive voltage, athinness, and lightness of weight, among others.

Since the thin film transistor (“TFT”) is significantly thinner than aconventional transistor, the process of manufacturing a TFT iscomplicated, resulting in low productivity and high manufacturing costs.In particular, since a mask is used in every step for manufacturing aTFT, at least seven masks are required. Therefore, various methods forincreasing productivity of the TFT and lowering the manufacturing costshave been studied. In particular, a method for reducing the number ofthe masks used during the manufacturing process has been widelyresearched.

FIGS. 1 to 5 are sectional views for explaining a conventional methodfor manufacturing an LCD, as disclosed in U.S. Pat. No. 5,054,887.

In the drawings, reference characters “A” and “B” denote a TFT area anda pad area, respectively. Referring to FIG. 1, after forming a firstmetal film by depositing pure Al on a transparent substrate 2, gatepatterns 4 and 4 a are formed out of the first metal film by performinga first photolithography on the first metal film. The gate patterns arethen used as a gate electrode 4 in the TFT area and as a gate pad 4 a inthe pad area.

As shown in FIG. 2, after forming by general photolithography a secondphotoresist pattern (not shown) that covers a portion of the pad area,an anodized film 6 is formed by oxidizing the first metal film using thephotoresist pattern as an anti-oxidation film. The anodized film 6 isthen formed on the entire surface of the gate electrode 4 formed in theTFT area, and on a portion of the gate pad 4 a in the pad area.

Referring to FIG. 3, an insulating film 8 is formed by depositing alayer such as a nitride film over the anodized film 6. A semiconductorfilm is then formed by subsequently depositing an amorphous silicon film10 and an amorphous silicon film 12 doped with impurities on the entiresurface of the substrate 2 on which the insulating film 8 is formed. Asemiconductor film pattern 10 and 12 to be used as an active portion isthen formed in the TFT area by performing a third photolithography onthe semiconductor film.

As shown in FIG. 4, a fourth photoresist pattern (not shown) is thenformed that exposes a portion of the gate pad 4 a formed in the pad areaby performing a fourth photolithography on the entire surface of thesubstrate 2 on which the semiconductor film pattern is formed. Then, acontact hole is then formed in the insulating film 8, which contact holeexposes a portion of the gate pad 4 a. The contact hole is formed byetching the insulating film 8 using the fourth photoresist pattern as amask. A source electrode 14 a and a drain electrode 14 b are then formedin the TFT area by depositing a chromium (“Cr”) film on the entiresurface of the substrate having the contact hole and performing a fifthphotolithography on the Cr film. In the pad area, a pad electrode 14 cconnected to the gate pad 4 a through the contact hole is formed. Atthis time, the impurity doped-amorphous silicon film 12 on the upperportion of the gate electrode 4 formed in the TFT area during thephotolithography process is partially etched, thus exposing a portion ofthe amorphous silicon film 10.

Referring to FIG. 5, a protection film 16 is then formed by depositingan oxide film over the entire surface of the substrate 2 on which thesource electrode 14 a, the drain electrode 14 b and the pad electrode 14c are formed. Then, contact holes are formed that expose a portion ofthe drain electrode 14 b of the TFT area and a portion of the padelectrode 14 c of the pad area. The contact holes are formed byperforming a sixth photolithography on the protection film 16.

Subsequently, pixel electrodes 18 and 18 a are formed by depositingindium tin oxide (“ITO”), a transparent conductive material, over theentire surface of the substrate, including the contact hole, andperforming a seventh photolithography process on the resultant ITO film.As a result of this seventh lithography, the drain electrode 14 b andthe pixel electrode 18 are connected in the TFT area, and the padelectrode 14 c and the pixel electrode 18 a are connected in the padarea.

According to the conventional method for manufacturing the LCD, purealuminum (“Al”) is used as the gate electrode material to lower theresistance of a gate line. An anodizing process is therefore required toprevent a hillock caused by the Al. This additional anodizing stepcomplicates the manufacturing process, reduces productivity, andincreases manufacturing costs.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved methodfor manufacturing a liquid crystal display in which manufacturing costsare reduced and productivity increased by reducing the number ofphotolithography processes performed.

It is another object of the present invention to provide a method formanufacturing a liquid crystal display by which it is possible toprevent the deterioration of device characteristics by preventing thegeneration of an undercut in a gate electrode.

To achieve the above objects, there is provided an improved method formanufacturing a liquid crystal display according to the presentinvention, comprising the steps of forming a gate electrode and a gatepad by a first photolithography process by sequentially depositing afirst metal film and a second metal film over a substrate of a TFT areaand a pad area, respectively; forming an insulating film over the entiresurface of the substrate on which the gate electrode and the gate padare formed; forming a semiconductor film pattern over the insulatingfilm of the TFT area using a second photolithography process; forming asource electrode and a drain electrode in the TFT area using a thirdphotolithography process, the source electrode and the drain electrodecomprising a third metal film; forming a protection film pattern overthe substrate on which the source electrode and the drain electrode areformed using a fourth photolithography process, the protection filmpattern exposing a portion of the drain electrode and a portion of thegate pad; and forming a pixel electrode over the substrate on which theprotection film pattern is formed using a fifth photolithographyprocess, the pixel electrode being connected to the drain electrode andthe gate pad.

The first metal film preferably comprises one of aluminum or an aluminumalloy and the second metal film comprises a refractory metal. Morespecifically, the second metal film preferably comprises a metalselected from the group consisting of Cr, Ta, Mo, and Ti.

The step of forming the gate electrode includes the steps of forming thefirst metal film and the second metal film over a substrate in thedescribed order; forming a photoresist pattern over a portion of thesecond metal film; etching the second metal film using the photoresistpattern as a mask; reflowing the photoresist pattern; etching the firstmetal film using the reflowed photoresist pattern as a mask; andremoving the reflowed photoresist pattern. The step of reflowing thephotoresist pattern may be performed in multiple steps.

The step of forming the gate electrode preferably includes the steps offorming the first metal film and the second metal film on the substratein the described order; forming a photoresist pattern on a portion ofthe second metal film; etching the second metal film by etching usingthe photoresist pattern as a mask; and etching the first metal film. Theetching of the second metal film may be either a wet or dry etch and astep of baking the photoresist pattern may be included after the step ofetching the second metal film.

The step of forming the gate electrode preferably includes the steps offorming the first metal film and the second metal film on a substrate;forming a photoresist pattern on a portion of the second metal film;etching the second metal film using the photoresist pattern as a mask;etching the first metal film using the patterned second metal film; andre-etching the patterned second metal film. A step of baking thephotoresist pattern may be included prior to the step of etching thefirst metal film after the step of etching the second metal film.

According to the present invention, it is possible to prevent a batteryeffect and a hillock caused by directly contact of Al to the ITO byforming the gate electrode in a double structure of Al or an Al alloyand a refractory metal film. Also, it is possible to omit the anodizingprocess and to simultaneously etch the insulating layer and theprotection film due to a capping film, thus reducing the number of thephotolithography processes. Also, since it is possible to form the firstmetal film larger than or identical to the second metal film, anundercut is not generated in the gate electrode. Therefore, it ispossible to prevent the deterioration of insulation characteristics dueto poor step coverage during deposition of the insulating film afterforming the gate electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail a preferred embodiment thereofwith reference to the attached drawings in which:

FIGS. 1 through 5 are sectional views illustrating a method formanufacturing liquid crystal display according to a conventional method;

FIG. 6 is a schematic plan view of the mask patterns used formanufacturing a liquid crystal display according to first through fourthpreferred embodiments of the present invention;

FIGS. 7 through 11 are sectional views illustrating a method formanufacturing a liquid crystal display according to a first preferredembodiment of the present invention;

FIG. 12 is a sectional view showing generation of an undercut in a gateelectrode;

FIGS. 13 through 16 are sectional views illustrating a method formanufacturing a liquid crystal display according to a second preferredembodiment of the present invention;

FIGS. 17 through 19 are sectional views illustrating a method formanufacturing a liquid crystal display according to a third preferredembodiment of the present invention; and

FIGS. 20 through 23 are sectional views illustrating a method formanufacturing a liquid crystal display according to a fourth preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 6 is a schematic plan view of the mask patterns used formanufacturing a liquid crystal display according to the presentinvention, in which reference numeral 100 denotes a mask pattern forforming a gateline; reference numeral 105 denotes a mask pattern forforming a gate pad; reference numeral 110 denotes a mask pattern forforming a data line, reference numeral 115 denotes a mask pattern forforming a data pad; reference numeral 120 denotes a mask pattern forforming a semiconductor film; reference numeral 130 denotes a maskpattern for forming a source electrode/drain electrode; referencenumeral 140 denotes a mask pattern for forming a contact hole forconnecting a pixel electrode to the drain electrode in the TFT area;reference numeral 145 denotes a mask pattern for forming a contact holefor connecting a gate pad in the pad area to the pixel electrode;reference numeral 150 denotes a mask pattern for forming a pixelelectrode in the TFT area; and reference numeral 155 denotes a maskpattern for forming a pixel electrode in the pad portion.

Referring to FIG. 6, the gate line 100 is arranged horizontally, and thedata line 110 is arranged perpendicular to the gate line. The pluralityof gate lines 100 and data lines 110 in the device are arranged togetherin a matrix pattern. The gate pad 105 is provided at the end portion ofthe gate line 100, and the data pad 115 is provided at the end portionof the data line 110. Pixel portions are respectively arranged in thematrix pattern in the portion bounded by the two adjacent gate lines andthe data line. The gate electrodes of the respective TFTs are formed soas to protrude into the pixel portions from the respective gate lines.The semiconductor film 120 is formed between the drain electrodes andthe gate electrodes of the respective TFTs. The source electrodes of theTFTs are formed in protruding portions from the data line 110. The pixelelectrodes 150 comprise transparent ITO and are formed in the respectivepixel portions.

FIGS. 7 through 11 are sectional views for explaining a method formanufacturing a liquid crystal display according to a first preferredembodiment of the present invention. Reference character “C” representsthe TFT area, which is a sectional view taken along I-I′ of FIG. 6, andreference character “D” represents the pad area, which is a sectionalview taken along II-II′ of FIG. 6.

FIG. 7 shows the steps for forming the gate electrode, in which a firstmetal film 22 is formed by depositing an Al or an Al-alloy film to athickness of 2,000˜4,000 Å over a transparent substrate 20. A secondmetal film 24 is then formed by depositing a refractory metal film to athickness 500˜2,000 Å over the first metal film. Gate patterns are thenformed in the TFT area and the pad area by performing a firstphotolithography on the first and the second metal films 22 and 24. Thegate patterns are used as a gate electrode in the TFT area and as a gatepad in the pad area. The first and the second metal films are then wetor dry etched using a mask.

The first metal film 22 is preferably formed of Al or an Al-alloy suchas Al—Nd or Al—Ta. It is possible to lower the resistance of the gateline and to prevent generation of a hillock when the gate electrode isformed of the Al alloy. The second metal film 24 is preferably formed ofone refractory metal selected from the group consisting of Cr, Ta, Mo,and Ti. The second metal film acts as a capping film to prevent the Alalloy from contacting the ITO film to be formed in a subsequent process.Because a capping film is formed on the Al or Al-alloy, a hightemperature oxidation process and a photolithography process for formingan oxidized film are not required. Also, since the second metal film 24does not include Al, no battery effect is generated, even though thesecond metal film 24 directly contacts the ITO film formed in asubsequent process.

FIG. 8 shows the steps for forming a semiconductor film pattern, inwhich an insulating film 26 is formed by depositing a nitride film to athickness of about 4,000 Å over the entire surface of the substrate onwhich a gate pattern is formed. A semiconductor film preferablycomprised of an amorphous silicon film 28 and an impuritydoped-amorphous silicon film 30 is formed to a thickness of 1,000˜2,000Å and a thickness of 500 Å, respectively, on the insulating layer 26. Asemiconductor film pattern to be used as an active area is then formedin the TFT area by performing a second photolithography on thesemiconductor film.

FIG. 9 shows the steps for forming a source electrode and a drainelectrode. A third metal film is formed by depositing a Cr film to athickness of 1,000˜2,000 Å over the entire surface of the substrate 20on which the semiconductor film pattern is formed. The third metal filmis preferably deposited using a sputtering method. A source electrode 32a and a drain electrode 32 b are then formed in the TFT area byperforming a third photolithography on the third metal film.

FIG. 10 shows the steps for forming a protection film pattern. Theprotection film 34 is formed by depositing an insulating material, e.g.,an oxide film to a thickness of 1,000˜3,000 Å over the entire surface ofthe substrate on which the source electrode 32 a and the drain electrode32 b are formed. A protection film pattern 34 is formed by performing afourth photolithography on the protection film. The protection filmpattern 34 exposes a portion of the drain electrode 32 b and a portionof the gate electrode 22 and 24 formed in the pad area, i.e., a gatepad. The protection film 34 and the insulating film 26 in the pad areaover the gate pad are simultaneously etched to expose a portion of thecapping film 24.

FIG. 11 shows the steps for forming a pixel electrode. After forming theITO film, a transparent conductive film, by a sputtering method over theentire surface of the substrate on which the protection film pattern isformed, pixel electrodes 36 and 36 a are formed in the TFT area and thepad area by performing a fifth photolithography on the ITO film. As aresult, the pixel electrode 36 and the drain electrode 32 b areconnected in the TFT area and the pixel electrode 36 a, and the gate pad22 and 24 are connected in the pad area.

The method for forming a liquid crystal display according to a firstembodiment of the present invention prevents the occurrence of a batteryeffect and prevents the formation of an Al hillock caused by contact ofAl to the ITO. This method achieves these goals by forming a gateelectrode using Al or an Al-alloy and by forming the capping film on thegate electrode using a refractory metal. The method of the firstpreferred embodiment also makes it possible to reduce the number ofphotolithography processes by omitting the anodizing process andsimultaneously forming the contact on the insulating film and theprotection film.

The first metal film 22 and the second metal film 24 which comprise thegate electrode in the first embodiment of the present invention areetched using only one mask. As a result of this use of a single mask, anundercut may be generated in the gate electrode as shown in FIG. 12. Asa result, step coverage becomes poor in a subsequent insulating filmdepositing process, thus creating a risk of deteriorating insulationcharacteristics. In the second through fourth embodiments of the presentinvention, a method for preventing the generation of the undercut in thegate electrode is provided.

FIGS. 13 through 16 are sectional views illustrating a method formanufacturing a liquid crystal display according to a second preferredembodiment of the present invention. The initial steps of the process,through the step of forming the gate electrode, are shown. Allsubsequent steps are similar to those shown for the first preferredembodiment in FIGS. 8 to 11.

FIG. 13 shows the step of forming the conductive films for the gateelectrode. Initially, a first metal film 42 is formed by depositing anAl film or an Al-alloy film on a transparent substrate 40 to a thicknessof 2,000˜4,000 Å. A second metal film 44, used as a capping film, isthen formed by depositing a refractory metal, such as Cr, Ta, Mo, or Ti,preferably Cr, over the first metal film 42. In this process, Al—Nd orAl—Ta may be used for the Al-alloy film.

FIG. 14 shows the step of forming a photoresist pattern 46. Aphotoresist pattern 46 is formed by coating photoresist over the secondmetal film 44 and by exposing and developing the photoresist. The secondmetal film 44 is then etched using the photoresist pattern 46 as a mask.An undercut is generated in the second metal film 44 during this etchingprocess by sufficiently overetching the second metal film 44.

FIG. 15 shows the step of reflowing the photoresist 46. The substrate isheated to a temperature above 100° C. to reflow the photoresist 46. Amultiple-step heat treatment may be performed on the substrate toimprove the reflow characteristic of the photoresist 46. As a result ofthe reflowing process, the reflowed photoresist 46 a completely coversthe patterned second metal film 44.

FIG. 16 shows the steps of forming the gate electrode. First, the firstmetal film 42 is etched using the reflowed photoresist pattern 46 a ofFIG. 15 as a mask, after which the reflowed photoresist 46 a is removed.Since the etched first metal film 42 is now wider than the second metalfilm 44 by the thickness of the reflowed photoresist 46 a of FIG. 15,the step coverage of the insulating film is favorable in a subsequentinsulating film depositing step. In order to prevent the first metalfilm 42 from contacting the ITO formed in a subsequent process, it ispreferable to control the thickness and the size of the photoresistpattern to make the patterned second metal film 44 larger than thecontact hole for connecting the ITO and the gate pad.

FIGS. 17 through 19 are sectional views for explaining a method formanufacturing a liquid crystal display according to a third preferredembodiment of the present invention. The initial steps of the process,through the step of forming the gate electrode, are shown. Allsubsequent steps are similar to those shown for the first preferredembodiment in FIGS. 8 to 11.

FIG. 17 shows the step of forming conductive films 52 and 54 for thegate electrode and a photoresist pattern 56. These steps are identicalto the steps described with reference to FIG. 13 for the secondpreferred embodiment of the present invention.

FIG. 18 shows the step of patterning the second metal film 54. In thisstep, the second metal film 54 is wet or dry etched using thephotoresist pattern 56 of FIG. 17 as a mask. The photoresist pattern maythen be removed, or it may remain until after the first metal film 52 isetched.

If the second metal film 54 is wet etched in this step, an undercut maybe generated to narrow the width of the first metal film 52. In thiscase, if the photoresist pattern is not removed, baking may be performedon the photoresist pattern to prevent lifting of the photoresistpattern.

FIG. 19 shows the step of forming the gate electrode by etching thefirst metal film 52 using the patterned second metal film 54 as a mask.If the photoresist pattern 56 is not removed in the previous step, thephotoresist pattern 56 can be used as a mask and it can be removed afteretching the first metal film 52.

FIGS. 20 through 23 are sectional views for explaining a method formanufacturing a liquid crystal display according to a fourth preferredembodiment of the present invention. The initial steps of the process,through the step of forming the gate electrode, are shown. Allsubsequent steps are similar to those shown for the first preferredembodiment in FIGS. 8 to 11.

FIG. 20 shows the steps of forming conductive films 62 and 64 for thegate electrode and a photoresist pattern 66. These steps are identicalto the steps described with reference to FIGS. 13 and 17 for the secondand third preferred embodiments of the present invention.

FIG. 21 shows the step of etching the second metal film, in which thesecond metal film 64 is wet etched using the photoresist pattern 66 as amask. At this time, the second metal film 64 is sufficiently etched soas to generate an undercut.

FIG. 22 shows the step of etching the first metal film 62. In this stepan undercut is formed in the gate electrode as shown in FIG. 12 when thefirst metal film 62 is wet etched using the patterned second metal film64 as a mask.

FIG. 23 shows the step of re-etching the second metal film, in which thewidth of the lower portion of the first metal film 62 becomes wider thanthat of the second metal film 64 after the patterned second metal film64 is re-etched. As a result of this re-etching, the undercut of thegate electrode is removed. To avoid lifting of the photoresist pattern66 when etching the first metal film 62 or when re-etching the secondmetal film 64, baking may be performed on the second metal film 64 afterperforming the first etching on the second metal film 64.

According to the above-mentioned preferred methods for manufacturing theliquid crystal display according to the present invention, the gateelectrode is formed in a two-layered-structure of Al or Al-alloy and arefractory metal. Therefore, it is possible to prevent a battery effectcaused by directly contacting the Al to the ITO and it is also possibleto prevent the generation of a hillock of the Al due to the stressrelaxation of the refractory metal. It is also possible to reduce thenumber of photolithography processes by omitting the anodizing processand simultaneously etching the insulating film and the protection film.

Since it is possible to form the Al film or Al-alloy film formed on thelower area to be identical in size or larger than the refractory metalformed on the upper portion, an undercut is not generated in the gateelectrode. Therefore, it is possible to prevent the deterioration ofinsulation characteristics caused by poor step coverage.

The present invention is not limited to the above-described embodiments.Various changes and modifications may be effected by one having anordinary skill in the art and remain within the scope of the invention,as defined by the appended claims.

What is claimed is:
 1. A method for manufacturing a TFT substrate, themethod comprising: (a) forming a gate electrode and a gate pad by afirst photolithography process by sequentially depositing a first metalfilm and a second metal film over a substrate in a TFT area and a padarea, respectively; (b) forming an insulating film over the entiresurface of the substrate on which the gate electrode and the gate padare formed; (c) forming a semiconductor film over the TFT area using asecond photolithography process; (d) forming a source electrode and adrain electrode in the TFT area using a third photolithography process,the source electrode and drain electrode comprising a third metal film;(e) forming a protection film pattern over the source electrode and thedrain electrode in the TFT area and over the insulating film in the gatepad area, using a fourth photolithography process, the protection filmpattern exposing a portion of the drain electrode and a top surface ofthe second metal film; and (f) forming a first and second pixelelectrode pattern over the substrate and the protection film patternusing a fifth photolithography process, the first pixel electrodepattern being connected to the drain electrode in the TFT area, and thesecond pixel electrode pattern being connected to the top surface of thesecond metal film of the gate pad in the pad area.
 2. A method formanufacturing a TFT substrate, as recited in claim 1, wherein the firstmetal film comprises aluminum or an aluminum alloy and the second metalfilm comprises a refractory metal.
 3. A method for manufacturing a TFTsubstrate, as recited in claim 2, wherein the second metal filmcomprises a metal selected from the group consisting of Cr, Mo, Ta, andTi.
 4. A method for manufacturing a TFT substrate, as recited in claim1, wherein the step (a) of forming the gate electrode further comprises:(a₁) forming the first metal film and the second metal film using aphotoresist as a mask; (a₂) forming a photoresist pattern over a portionof the second metal film; (a₃) etching the second metal film using thephotoresist pattern as a mask; (a₄) reflowing the photoresist pattern;(a₅) etching the first metal film using the reflowed photoresist patternas a mask; and (a₆) removing the reflowed photoresist pattern.
 5. Amethod for manufacturing a TFT substrate, as recited in claim 4, whereinthe second metal film is overetched in the step (a₃) of etching thesecond metal film to generate an undercut.
 6. A method for manufacturinga TFT substrate, as recited in claim 4, wherein step (a₄) of reflowingthe photoresist pattern is performed in multiple steps.
 7. A method formanufacturing a TFT substrate, as recited in claim 1, wherein the step(a) of forming the gate electrode further comprises: (a₁′) forming thefirst metal film and the second metal film over the substrate in thedescribed order; (a₂′) forming a photoresist pattern over a portion ofthe second metal film; (a₃′) etching the second metal film using thephotoresist pattern as a mask; and (a₄′) etching the first metal film.8. A method for manufacturing a TFT substrate, as recited in claim 7,wherein the step (a₃′) of etching the second metal film is performed bywet etching.
 9. A method for manufacturing a TFT substrate, as recitedin claim 7, wherein the step (a₃′) of etching the second metal film isperformed by dry etching.
 10. A method for manufacturing a TFTsubstrate, as recited in claim 7, further comprising baking thephotoresist pattern after the step (a₃′) of etching the second metalfilm.
 11. A method for manufacturing a TFT substrate, as recited inclaim 1, wherein the step (a) of forming the gate electrode furthercomprises: (a₁″) forming the first metal film and the second metal filmover the substrate; (a₂″) forming a photoresist pattern over a portionof the second metal film; (a₃″) etching the second metal film using thephotoresist pattern as a mask; (a₄″) etching the first metal film usingthe patterned second metal film as a mask; and (a₅″) re-etching thepatterned second metal film.
 12. A method for manufacturing a TFTsubstrate, as recited in claim 11, further comprising baking thephotoresist pattern prior to step (a₄″) of etching the first metal film.13. A method for manufacturing a TFT substrate, the method comprisingthe steps of: (a) forming a gate electrode and a gate pad bysequentially depositing a first metal film selected from the group of Aland Al-alloy, and a second metal film over a substrate of a TFT area anda pad area, respectively and then patterning the first and second metalfilms by a first photolithography process; (b) forming a firstinsulating film over the entire surface of the substrate on which thegate electrode and the gate pad are formed; (c) forming a patternedsemiconductor film over the first insulating film in the TFT area bydepositing an amorphous silicon film and a doped amorphous silicon filmand patterning the amorphous silicon film and the doped amorphoussilicon film by a second photolithography process; (d) forming a sourceelectrode and a drain electrode in the TFT area by depositing a thirdmetal film and then patterning the third metal film by a thirdphotolithography process; (e) etching the doped amorphous silicon filmbetween the source electrode and the drain electrode; (f) forming aprotection film over the source and drain electrodes in the TFT area andover the first insulating film in the gate pad region by depositing asecond insulating film over the source and drain electrodes in the TFTarea and over the first insulating film in the gate pad region and thenetching away the second insulating film over a first portion of thedrain electrode and over a second portion of the gate pad; (g) etchingaway the first insulating film over the second portion of the gate pad;and (h) forming a first and second pixel electrode pattern over thesubstrate and the protection film pattern using a fifth photolithographyprocess, the first pixel electrode pattern being connected to the drainelectrode in the TFT area, and the second pixel electrode pattern beingconnected to the top surface of the second metal film of the gate pad inthe pad area.